Shadowmere Cavern is a subterranean site in Tadrium associated with the Ariessus family and Luther Mortanas. In the period leading up to 8751 SE, the Ariessus family used the cavern to harvest a substance they called motes of shadow for Mortanas as part of their dealings with him.
The Brass Blades reached Shadowmere while investigating those dealings after the destruction of their original headquarters in Elgaard. Darieth Ariessus encountered a being within the cavern that severed or removed the pact through which he had previously possessed shadow-touched powers. Those powers did not return afterward.
The surviving accounts establish the cavern’s role in Mortanas’s network but do not clearly explain the nature of the motes, the identity of the being encountered by Darieth, or why Shadowmere possessed the properties that made the harvesting possible. The site is therefore better documented as part of the Ariessus and Mortanas history than as a well-understood natural or magical phenomenon.